summaryrefslogtreecommitdiff
path: root/tools/sk-libfido2.c
blob: 15aa813aab77a6c038db14114f0277b228ddf7a3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
/*
 * Copyright (c) 2019 Markus Friedl
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <fcntl.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stddef.h>
#include <stdarg.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#ifdef WITH_OPENSSL
#include <openssl/opensslv.h>
#include <openssl/crypto.h>
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#endif /* WITH_OPENSSL */

#include <fido.h>

#ifndef SK_STANDALONE
#include "log.h"
#include "xmalloc.h"
#endif

/* #define SK_DEBUG 1 */

#if defined(_WIN32)
#include <windows.h>
#include <winternl.h>
#include <winerror.h>
#include <bcrypt.h>
#include <sal.h>
#endif 

#define MAX_FIDO_DEVICES	256

/* Compatibility with OpenSSL 1.0.x */
#if (OPENSSL_VERSION_NUMBER < 0x10100000L)
#define ECDSA_SIG_get0(sig, pr, ps) \
	do { \
		(*pr) = sig->r; \
		(*ps) = sig->s; \
	} while (0)
#endif

#define SK_VERSION_MAJOR	0x00020000 /* current API version */

/* Flags */
#define SK_USER_PRESENCE_REQD	0x01

/* Algs */
#define	SK_ECDSA		0x00
#define	SK_ED25519		0x01

struct sk_enroll_response {
	uint8_t *public_key;
	size_t public_key_len;
	uint8_t *key_handle;
	size_t key_handle_len;
	uint8_t *signature;
	size_t signature_len;
	uint8_t *attestation_cert;
	size_t attestation_cert_len;
};

struct sk_sign_response {
	uint8_t flags;
	uint32_t counter;
	uint8_t *sig_r;
	size_t sig_r_len;
	uint8_t *sig_s;
	size_t sig_s_len;
};

/* If building as part of OpenSSH, then rename exported functions */
#if !defined(SK_STANDALONE)
#define sk_api_version	ssh_sk_api_version
#define sk_enroll	ssh_sk_enroll
#define sk_sign		ssh_sk_sign
#endif

/* Return the version of the middleware API */
uint32_t sk_api_version(void);

/* Enroll a U2F key (private key generation) */
int sk_enroll(int alg, const uint8_t *challenge, size_t challenge_len,
    const char *application, uint8_t flags,
    struct sk_enroll_response **enroll_response);

/* Sign a challenge */
int sk_sign(int alg, const uint8_t *message, size_t message_len,
    const char *application, const uint8_t *key_handle, size_t key_handle_len,
    uint8_t flags, struct sk_sign_response **sign_response);

#ifdef SK_DEBUG
static void skdebug(const char *func, const char *fmt, ...)
    __attribute__((__format__ (printf, 2, 3)));

static void
skdebug(const char *func, const char *fmt, ...)
{
#if !defined(SK_STANDALONE)
	char *msg;
	va_list ap;

	va_start(ap, fmt);
	xvasprintf(&msg, fmt, ap);
	va_end(ap);
	debug("%s: %s", func, msg);
	free(msg);
#else
	va_list ap;

	va_start(ap, fmt);
	fprintf(stderr, "%s: ", func);
	vfprintf(stderr, fmt, ap);
	fputc('\n', stderr);
	va_end(ap);
#endif /* !SK_STANDALONE */
}
#else
#define skdebug(...) do { /* nothing */ } while (0)
#endif /* SK_DEBUG */

uint32_t
sk_api_version(void)
{
	return SK_VERSION_MAJOR;
}

/* Select the first identified FIDO device attached to the system */
static char *
pick_first_device(void)
{
	char *ret = NULL;
	fido_dev_info_t *devlist = NULL;
	size_t olen = 0;
	int r;
	const fido_dev_info_t *di;

	if ((devlist = fido_dev_info_new(1)) == NULL) {
		skdebug(__func__, "fido_dev_info_new failed");
		goto out;
	}
	if ((r = fido_dev_info_manifest(devlist, 1, &olen)) != FIDO_OK) {
		skdebug(__func__, "fido_dev_info_manifest failed: %s",
		    fido_strerr(r));
		goto out;
	}
	if (olen != 1) {
		skdebug(__func__, "fido_dev_info_manifest bad len %zu", olen);
		goto out;
	}
	di = fido_dev_info_ptr(devlist, 0);
	if ((ret = strdup(fido_dev_info_path(di))) == NULL) {
		skdebug(__func__, "fido_dev_info_path failed");
		goto out;
	}
 out:
	fido_dev_info_free(&devlist, 1);
	return ret;
}

#if defined(HAVE_ARC4RANDOM_BUF)
static int
get_random_challenge(uint8_t *ptr, size_t len)
{
	arc4random_buf(ptr, len);

	return 0;
}
#elif defined(HAVE_GETENTROPY)
static int
get_random_challenge(uint8_t *ptr, size_t len)
{
	if (getentropy(ptr, len) == -1) {
		skdebug(__func__, "getentropy failed");
		return -1;
	}

	return 0;
}
#elif defined(HAS_DEV_URANDOM)
static int
get_random_challenge(uint8_t *ptr, size_t len)
{
	int fd;
	ssize_t n;

	if ((fd = open(FIDO_RANDOM_DEV, O_RDONLY)) < 0) {
		skdebug(__func__, "open %s failed", FIDO_RANDOM_DEV);
		return -1;
	}

	n = read(fd, ptr, len);
	close(fd);

	if (n < 0 || (size_t)n != len) {
		skdebug(__func__, "read from %s failed", FIDO_RANDOM_DEV);
		return -1;
	}

	return 0;
}
#elif defined(_WIN32)
static int
get_random_challenge(uint8_t *ptr, size_t len)
{
	NTSTATUS status;

	status = BCryptGenRandom(NULL, ptr, len,
	    BCRYPT_USE_SYSTEM_PREFERRED_RNG);
	if (!NT_SUCCESS(status))
		return -1;

	return 0;
}
#else
#error "please provide an implementation of get_random_challenge() for your platform"
#endif

/* Check if the specified key handle exists on a given device. */
static int
try_device(fido_dev_t *dev, const char *application,
    const uint8_t *key_handle, size_t key_handle_len)
{
	fido_assert_t *assert = NULL;
	uint8_t challenge[32];
	int r = FIDO_ERR_INTERNAL;

	if (get_random_challenge(challenge, sizeof(challenge)) == -1) {
		skdebug(__func__, "get_random_challenge failed");
		goto out;
	}

	if ((assert = fido_assert_new()) == NULL) {
		skdebug(__func__, "fido_assert_new failed");
		goto out;
	}
	if ((r = fido_assert_set_clientdata_hash(assert, challenge,
	    sizeof(challenge))) != FIDO_OK) {
		skdebug(__func__, "fido_assert_set_clientdata_hash: %s",
		    fido_strerr(r));
		goto out;
	}
	if ((r = fido_assert_set_rp(assert, application)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_set_rp: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_assert_allow_cred(assert, key_handle,
	    key_handle_len)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_allow_cred: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_assert_set_up(assert, FIDO_OPT_FALSE)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_up: %s", fido_strerr(r));
		goto out;
	}
	r = fido_dev_get_assert(dev, assert, NULL);
	skdebug(__func__, "fido_dev_get_assert: %s", fido_strerr(r));
	if (r == FIDO_ERR_USER_PRESENCE_REQUIRED) {
		/* U2F tokens may return this */
		r = FIDO_OK;
	}
 out:
	fido_assert_free(&assert);

	return r != FIDO_OK ? -1 : 0;
}

/* Iterate over configured devices looking for a specific key handle */
static fido_dev_t *
find_device(const char *application, const uint8_t *key_handle,
    size_t key_handle_len)
{
	fido_dev_info_t *devlist = NULL;
	fido_dev_t *dev = NULL;
	size_t devlist_len = 0, i;
	const char *path;
	int r;

	if ((devlist = fido_dev_info_new(MAX_FIDO_DEVICES)) == NULL) {
		skdebug(__func__, "fido_dev_info_new failed");
		goto out;
	}
	if ((r = fido_dev_info_manifest(devlist, MAX_FIDO_DEVICES,
	    &devlist_len)) != FIDO_OK) {
		skdebug(__func__, "fido_dev_info_manifest: %s", fido_strerr(r));
		goto out;
	}

	skdebug(__func__, "found %zu device(s)", devlist_len);

	for (i = 0; i < devlist_len; i++) {
		const fido_dev_info_t *di = fido_dev_info_ptr(devlist, i);

		if (di == NULL) {
			skdebug(__func__, "fido_dev_info_ptr %zu failed", i);
			continue;
		}
		if ((path = fido_dev_info_path(di)) == NULL) {
			skdebug(__func__, "fido_dev_info_path %zu failed", i);
			continue;
		}
		skdebug(__func__, "trying device %zu: %s", i, path);
		if ((dev = fido_dev_new()) == NULL) {
			skdebug(__func__, "fido_dev_new failed");
			continue;
		}
		if ((r = fido_dev_open(dev, path)) != FIDO_OK) {
			skdebug(__func__, "fido_dev_open failed");
			fido_dev_free(&dev);
			continue;
		}
		if (try_device(dev, application, key_handle,
		    key_handle_len) == 0) {
			skdebug(__func__, "found key");
			break;
		}
		fido_dev_close(dev);
		fido_dev_free(&dev);
	}

 out:
	if (devlist != NULL)
		fido_dev_info_free(&devlist, MAX_FIDO_DEVICES);

	return dev;
}

#ifdef WITH_OPENSSL
/*
 * The key returned via fido_cred_pubkey_ptr() is in affine coordinates,
 * but the API expects a SEC1 octet string.
 */
static int
pack_public_key_ecdsa(fido_cred_t *cred, struct sk_enroll_response *response)
{
	const uint8_t *ptr;
	BIGNUM *x = NULL, *y = NULL;
	EC_POINT *q = NULL;
	EC_GROUP *g = NULL;
	int ret = -1;

	response->public_key = NULL;
	response->public_key_len = 0;

	if ((x = BN_new()) == NULL ||
	    (y = BN_new()) == NULL ||
	    (g = EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1)) == NULL ||
	    (q = EC_POINT_new(g)) == NULL) {
		skdebug(__func__, "libcrypto setup failed");
		goto out;
	}
	if ((ptr = fido_cred_pubkey_ptr(cred)) == NULL) {
		skdebug(__func__, "fido_cred_pubkey_ptr failed");
		goto out;
	}
	if (fido_cred_pubkey_len(cred) != 64) {
		skdebug(__func__, "bad fido_cred_pubkey_len %zu",
		    fido_cred_pubkey_len(cred));
		goto out;
	}

	if (BN_bin2bn(ptr, 32, x) == NULL ||
	    BN_bin2bn(ptr + 32, 32, y) == NULL) {
		skdebug(__func__, "BN_bin2bn failed");
		goto out;
	}
	if (EC_POINT_set_affine_coordinates_GFp(g, q, x, y, NULL) != 1) {
		skdebug(__func__, "EC_POINT_set_affine_coordinates_GFp failed");
		goto out;
	}
	response->public_key_len = EC_POINT_point2oct(g, q,
	    POINT_CONVERSION_UNCOMPRESSED, NULL, 0, NULL);
	if (response->public_key_len == 0 || response->public_key_len > 2048) {
		skdebug(__func__, "bad pubkey length %zu",
		    response->public_key_len);
		goto out;
	}
	if ((response->public_key = malloc(response->public_key_len)) == NULL) {
		skdebug(__func__, "malloc pubkey failed");
		goto out;
	}
	if (EC_POINT_point2oct(g, q, POINT_CONVERSION_UNCOMPRESSED,
	    response->public_key, response->public_key_len, NULL) == 0) {
		skdebug(__func__, "EC_POINT_point2oct failed");
		goto out;
	}
	/* success */
	ret = 0;
 out:
	if (ret != 0 && response->public_key != NULL) {
		memset(response->public_key, 0, response->public_key_len);
		free(response->public_key);
		response->public_key = NULL;
	}
	EC_POINT_free(q);
	EC_GROUP_free(g);
	BN_clear_free(x);
	BN_clear_free(y);
	return ret;
}
#endif /* WITH_OPENSSL */

static int
pack_public_key_ed25519(fido_cred_t *cred, struct sk_enroll_response *response)
{
	const uint8_t *ptr;
	size_t len;
	int ret = -1;

	response->public_key = NULL;
	response->public_key_len = 0;

	if ((len = fido_cred_pubkey_len(cred)) != 32) {
		skdebug(__func__, "bad fido_cred_pubkey_len len %zu", len);
		goto out;
	}
	if ((ptr = fido_cred_pubkey_ptr(cred)) == NULL) {
		skdebug(__func__, "fido_cred_pubkey_ptr failed");
		goto out;
	}
	response->public_key_len = len;
	if ((response->public_key = malloc(response->public_key_len)) == NULL) {
		skdebug(__func__, "malloc pubkey failed");
		goto out;
	}
	memcpy(response->public_key, ptr, len);
	ret = 0;
 out:
	if (ret != 0)
		free(response->public_key);
	return ret;
}

static int
pack_public_key(int alg, fido_cred_t *cred, struct sk_enroll_response *response)
{
	switch(alg) {
#ifdef WITH_OPENSSL
	case SK_ECDSA:
		return pack_public_key_ecdsa(cred, response);
#endif /* WITH_OPENSSL */
	case SK_ED25519:
		return pack_public_key_ed25519(cred, response);
	default:
		return -1;
	}
}

int
sk_enroll(int alg, const uint8_t *challenge, size_t challenge_len,
    const char *application, uint8_t flags,
    struct sk_enroll_response **enroll_response)
{
	fido_cred_t *cred = NULL;
	fido_dev_t *dev = NULL;
	const uint8_t *ptr;
	uint8_t user_id[32];
	struct sk_enroll_response *response = NULL;
	size_t len;
	int cose_alg;
	int ret = -1;
	int r;
	char *device = NULL;

	(void)flags; /* XXX; unused */
#ifdef SK_DEBUG
	fido_init(FIDO_DEBUG);
#endif
	if (enroll_response == NULL) {
		skdebug(__func__, "enroll_response == NULL");
		goto out;
	}
	*enroll_response = NULL;
	switch(alg) {
#ifdef WITH_OPENSSL
	case SK_ECDSA:
		cose_alg = COSE_ES256;
		break;
#endif /* WITH_OPENSSL */
	case SK_ED25519:
		cose_alg = COSE_EDDSA;
		break;
	default:
		skdebug(__func__, "unsupported key type %d", alg);
		goto out;
	}
	if ((device = pick_first_device()) == NULL) {
		skdebug(__func__, "pick_first_device failed");
		goto out;
	}
	skdebug(__func__, "using device %s", device);
	if ((cred = fido_cred_new()) == NULL) {
		skdebug(__func__, "fido_cred_new failed");
		goto out;
	}
	memset(user_id, 0, sizeof(user_id));
	if ((r = fido_cred_set_type(cred, cose_alg)) != FIDO_OK) {
		skdebug(__func__, "fido_cred_set_type: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_cred_set_clientdata_hash(cred, challenge,
	    challenge_len)) != FIDO_OK) {
		skdebug(__func__, "fido_cred_set_clientdata_hash: %s",
		    fido_strerr(r));
		goto out;
	}
	if ((r = fido_cred_set_user(cred, user_id, sizeof(user_id),
	    "openssh", "openssh", NULL)) != FIDO_OK) {
		skdebug(__func__, "fido_cred_set_user: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_cred_set_rp(cred, application, NULL)) != FIDO_OK) {
		skdebug(__func__, "fido_cred_set_rp: %s", fido_strerr(r));
		goto out;
	}
	if ((dev = fido_dev_new()) == NULL) {
		skdebug(__func__, "fido_dev_new failed");
		goto out;
	}
	if ((r = fido_dev_open(dev, device)) != FIDO_OK) {
		skdebug(__func__, "fido_dev_open: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_dev_make_cred(dev, cred, NULL)) != FIDO_OK) {
		skdebug(__func__, "fido_dev_make_cred: %s", fido_strerr(r));
		goto out;
	}
	if (fido_cred_x5c_ptr(cred) != NULL) {
		if ((r = fido_cred_verify(cred)) != FIDO_OK) {
			skdebug(__func__, "fido_cred_verify: %s",
			    fido_strerr(r));
			goto out;
		}
	} else {
		skdebug(__func__, "self-attested credential");
		if ((r = fido_cred_verify_self(cred)) != FIDO_OK) {
			skdebug(__func__, "fido_cred_verify_self: %s",
			    fido_strerr(r));
			goto out;
		}
	}
	if ((response = calloc(1, sizeof(*response))) == NULL) {
		skdebug(__func__, "calloc response failed");
		goto out;
	}
	if (pack_public_key(alg, cred, response) != 0) {
		skdebug(__func__, "pack_public_key failed");
		goto out;
	}
	if ((ptr = fido_cred_id_ptr(cred)) != NULL) {
		len = fido_cred_id_len(cred);
		if ((response->key_handle = calloc(1, len)) == NULL) {
			skdebug(__func__, "calloc key handle failed");
			goto out;
		}
		memcpy(response->key_handle, ptr, len);
		response->key_handle_len = len;
	}
	if ((ptr = fido_cred_sig_ptr(cred)) != NULL) {
		len = fido_cred_sig_len(cred);
		if ((response->signature = calloc(1, len)) == NULL) {
			skdebug(__func__, "calloc signature failed");
			goto out;
		}
		memcpy(response->signature, ptr, len);
		response->signature_len = len;
	}
	if ((ptr = fido_cred_x5c_ptr(cred)) != NULL) {
		len = fido_cred_x5c_len(cred);
		if ((response->attestation_cert = calloc(1, len)) == NULL) {
			skdebug(__func__, "calloc attestation cert failed");
			goto out;
		}
		memcpy(response->attestation_cert, ptr, len);
		response->attestation_cert_len = len;
	}
	*enroll_response = response;
	response = NULL;
	ret = 0;
 out:
	free(device);
	if (response != NULL) {
		free(response->public_key);
		free(response->key_handle);
		free(response->signature);
		free(response->attestation_cert);
		free(response);
	}
	if (dev != NULL) {
		fido_dev_close(dev);
		fido_dev_free(&dev);
	}
	if (cred != NULL) {
		fido_cred_free(&cred);
	}
	return ret;
}

#ifdef WITH_OPENSSL
static int
pack_sig_ecdsa(fido_assert_t *assert, struct sk_sign_response *response)
{
	ECDSA_SIG *sig = NULL;
	const BIGNUM *sig_r, *sig_s;
	const unsigned char *cp;
	size_t sig_len;
	int ret = -1;

	cp = fido_assert_sig_ptr(assert, 0);
	sig_len = fido_assert_sig_len(assert, 0);
	if ((sig = d2i_ECDSA_SIG(NULL, &cp, sig_len)) == NULL) {
		skdebug(__func__, "d2i_ECDSA_SIG failed");
		goto out;
	}
	ECDSA_SIG_get0(sig, &sig_r, &sig_s);
	response->sig_r_len = BN_num_bytes(sig_r);
	response->sig_s_len = BN_num_bytes(sig_s);
	if ((response->sig_r = calloc(1, response->sig_r_len)) == NULL ||
	    (response->sig_s = calloc(1, response->sig_s_len)) == NULL) {
		skdebug(__func__, "calloc signature failed");
		goto out;
	}
	BN_bn2bin(sig_r, response->sig_r);
	BN_bn2bin(sig_s, response->sig_s);
	ret = 0;
 out:
	ECDSA_SIG_free(sig);
	if (ret != 0) {
		free(response->sig_r);
		free(response->sig_s);
		response->sig_r = NULL;
		response->sig_s = NULL;
	}
	return ret;
}
#endif /* WITH_OPENSSL */

static int
pack_sig_ed25519(fido_assert_t *assert, struct sk_sign_response *response)
{
	const unsigned char *ptr;
	size_t len;
	int ret = -1;

	ptr = fido_assert_sig_ptr(assert, 0);
	len = fido_assert_sig_len(assert, 0);
	if (len != 64) {
		skdebug(__func__, "bad length %zu", len);
		goto out;
	}
	response->sig_r_len = len;
	if ((response->sig_r = calloc(1, response->sig_r_len)) == NULL) {
		skdebug(__func__, "calloc signature failed");
		goto out;
	}
	memcpy(response->sig_r, ptr, len);
	ret = 0;
 out:
	if (ret != 0) {
		free(response->sig_r);
		response->sig_r = NULL;
	}
	return ret;
}

static int
pack_sig(int alg, fido_assert_t *assert, struct sk_sign_response *response)
{
	switch(alg) {
#ifdef WITH_OPENSSL
	case SK_ECDSA:
		return pack_sig_ecdsa(assert, response);
#endif /* WITH_OPENSSL */
	case SK_ED25519:
		return pack_sig_ed25519(assert, response);
	default:
		return -1;
	}
}

int
sk_sign(int alg, const uint8_t *message, size_t message_len,
    const char *application,
    const uint8_t *key_handle, size_t key_handle_len,
    uint8_t flags, struct sk_sign_response **sign_response)
{
	fido_assert_t *assert = NULL;
	fido_dev_t *dev = NULL;
	struct sk_sign_response *response = NULL;
	int ret = -1;
	int r;

#ifdef SK_DEBUG
	fido_init(FIDO_DEBUG);
#endif

	if (sign_response == NULL) {
		skdebug(__func__, "sign_response == NULL");
		goto out;
	}
	*sign_response = NULL;
	if ((dev = find_device(application, key_handle,
	    key_handle_len)) == NULL) {
		skdebug(__func__, "couldn't find device for key handle");
		goto out;
	}
	if ((assert = fido_assert_new()) == NULL) {
		skdebug(__func__, "fido_assert_new failed");
		goto out;
	}
	if ((r = fido_assert_set_clientdata_hash(assert, message,
	    message_len)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_set_clientdata_hash: %s",
		    fido_strerr(r));
		goto out;
	}
	if ((r = fido_assert_set_rp(assert, application)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_set_rp: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_assert_allow_cred(assert, key_handle,
	    key_handle_len)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_allow_cred: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_assert_set_up(assert,
	    (flags & SK_USER_PRESENCE_REQD) ?
	    FIDO_OPT_TRUE : FIDO_OPT_FALSE)) != FIDO_OK) {
		skdebug(__func__, "fido_assert_set_up: %s", fido_strerr(r));
		goto out;
	}
	if ((r = fido_dev_get_assert(dev, assert, NULL)) != FIDO_OK) {
		skdebug(__func__, "fido_dev_get_assert: %s", fido_strerr(r));
		goto out;
	}
	if ((response = calloc(1, sizeof(*response))) == NULL) {
		skdebug(__func__, "calloc response failed");
		goto out;
	}
	response->flags = fido_assert_flags(assert, 0);
	response->counter = fido_assert_sigcount(assert, 0);
	if (pack_sig(alg, assert, response) != 0) {
		skdebug(__func__, "pack_sig failed");
		goto out;
	}
	*sign_response = response;
	response = NULL;
	ret = 0;
 out:
	if (response != NULL) {
		free(response->sig_r);
		free(response->sig_s);
		free(response);
	}
	if (dev != NULL) {
		fido_dev_close(dev);
		fido_dev_free(&dev);
	}
	if (assert != NULL) {
		fido_assert_free(&assert);
	}
	return ret;
}